Thermal spraying is widely used to apply metals and ceramics in a form of coating or bulk materials on different types of substrates. A majority of thermal spray methods utilize energy of hot gaseous jets to heat and accelerate particles of spraying material. When impinging the substrate, the particles form a coating.
The particles of material to be sprayed, such a metal or ceramic, are provided to the thermal spray apparatus as a powder. A powder feeding apparatus is used to provide a controlled amount of powder to the thermal spray apparatus. Conventional powder feeding apparatuses have several shortcomings, such as wearing seals and non-uniform powder metering. Wearing seals are a common feature of conventional powder feeding apparatus design, and necessitate frequent replacement of seals to prevent formation of gaps and maintain proper operation. When used with abrasive powders, some powder feeders require seal replacement as often as every few hours. This not only adds to operating costs, but also has a disadvantage of necessitating the removal of the powder feeder from service in order to perform the required maintenance, effectively shutting down the entire thermal spray coating application process until the powder feeder maintenance is performed. Another shortcoming of conventional powder feeding apparatus design is the pulsation of the powder stream, which results from discrete metering of the powder material. Conventional metering mechanisms generally utilize slots or holes of fixed volume, into which the powder material is packed, and from which the powder material is dispensed into the powder stream in batches, resulting in a non-uniform powder stream.